Surgical needles are typically made from conventional metals such as surgical stainless steels and other biocompatible metal alloys. The needles desirably have smooth outer surfaces to facilitate the passage through tissue and minimize the adherence of contaminants or foreign substances. The needle surfaces are typically polished to provide smooth surfaces that are bright, shiny and reflective. Surgical needles are typically coated with silicone coatings to improve the penetration of the needles through multiple passes in tissue.
In certain types of surgical procedures such as endoscopic and laparoscopic surgical procedures, the surgeon views the site of the procedure remotely via a camera and a screen display of the surgical field. It is known that in such procedures the surgical team may have difficulty in seeing a conventional surgical needle because of the shiny reflective surfaces. This is particularly true of the distal end of the needle having the tissue piercing point. The inability to quickly and efficiently locate the needle and needle tip when conducting a laparoscopic suturing procedure has led to the development of surgical needles having blackened surfaces. The blackened needles have proven to have better visibility in the surgical field and are often preferred in minimally invasive surgical procedures utilizing indirect visualization.
Blackening processes for blackening the bright, shiny surfaces of surgical needles are known in this art. The processes may include chemical baths, exposure to plasmas, laser energy, oxidizing fumes, etc. The objective of the blackening processes is to form an iron oxide (Fe2O4)-based layer on the surfaces of the stainless steel needles which provides the blackened appearance.
The chemical baths used in the prior art processes typically contain Chromium (VI) as a component of the baths. Such processes are often lengthy and typically require process times in excess of twenty hours to provide effectively blackened surfaces on the needles.
Although the chemical needle blackening processes of the prior art are effective in providing blackened surfaces on surgical needles, there are known deficiencies associated with their use. First of all, the use of blackening baths containing the requisite high concentrations of Chromium (VI) compounds presents both environmental risks and safety hazards. The safety hazards include the carcinogenicity of the Chromium (VI) compounds. Chronic inhalation of hexavalent chromium compounds is known to increase the risk of lung cancer. (The lungs are the most vulnerable, followed by the fine capillaries in kidneys and intestines). Soluble Chromium (VI) compounds in conventional needle blackening solutions can cause or exacerbate contact dermatitis. Ingestion of chromium VI can also cause irritation or ulcers in the stomach and intestines. The environmental risks associated with Chromium (VI)-containing blackening baths include ground water and soil contamination, which leads to the risk of exposure to humans, domestic and farm animals, and wildlife. In addition to the safety hazards and environmental risks associated with such processes, it is known that the existing processes are extremely slow, typically requiring process times in excess of 20 hours up to 36 hours in order to achieve sufficiently effective blackening. This necessitates that such blackening processes are batch-type processes in which larger batches of needles are immersed in the blackening baths. The conventional processes cannot be used with high speed needle manufacturing processes wherein needles are mounted to strips and moved at a relatively high rate of speed to and from various manufacturing steps. Finally, the existing processes are not cost effective for a variety of reasons including production efficiency, generation and disposal of hazardous waste, burdensome engineering controls, substantial safety requirements, potential liability, etc.
Accordingly, there is a need in this art for novel methods and processes for blackening surgical needles that eliminate the need for Chromium (VI) compounds in blackening baths. There is a further need for blackening methods and processes that provide quick process times, are environmentally friendly, safe to operate, and are cost effective.